| Branch | Status |
|---|---|
| Master | |
| Dev |
Simple CQRS library
This project composes of components for implementing the CQRS pattern (Query Handling). This library was built with simplicity, modularity and pluggability in mind.
- Send queries to registered query handler.
- Multiple ways of registering handlers:
- Simple handler registration (no IoC container).
- IoC container registration - achieved by creating implementations of IContainerAdapter.
- Attribute registration - achieved by marking methods with [QueryHandler] attributes.
You can simply clone this repository, build the source, reference the dll from the project, and code away!
Xer.Cqrs libraries are also available as Nuget packages:
To install Nuget packages:
- Open command prompt
- Go to project directory
- Add the packages to the project:
dotnet add package Xer.Cqrs.QueryStack
- Restore the packages:
dotnet restore
(Samples are in ASP.NET Core)
// Example query.
public class QueryProductById : IQuery<Product>
{
public int ProductId { get; }
public QueryProductById(int productId)
{
ProductId = productId;
}
}
// Async query handler.
public class QueryProductByIdHandler : IQueryAsyncHandler<QueryProductById, Product>
{
private readonly IProductReadSideRepository _productRepository;
public QueryProductByIdHandler(IProductReadSideRepository productRepository)
{
_productRepository = productRepository;
}
public Task<Product> HandleAsync(QueryProductById query, CancellationToken cancellationToken = default(CancellationToken))
{
return _productRepository.GetProductByIdAsync(query.ProductId);
}
}
// Sync query handler.
public class SyncQueryProductByIdHandler : IQueryHandler<QueryProductById, Product>
{
private readonly IProductReadSideRepository _productRepository;
public QueryProductByIdHandler(IProductReadSideRepository productRepository)
{
_productRepository = productRepository;
}
public Product Handle(QueryProductById query)
{
return _productRepository.GetProductById(query.ProductId);
}
}
// Attributed query handler.
public class QueryProductByIdHandler
{
private readonly IProductReadSideRepository _productRepository;
public QueryProductByIdHandler(IProductReadSideRepository productRepository)
{
_productRepository = productRepository;
}
[QueryHandler]
public Product Handle(QueryProductById query)
{
return _productRepository.GetProductById(query.ProductId);
}
}Before we can dispatch any queries, first, we need to register our query handlers. There are several ways to do this:
// This method gets called by the runtime. Use this method to add services to the container.
public void ConfigureServices(IServiceCollection services)
{
...
// Read-side repository.
services.AddSingleton<IProductReadSideRepository, InMemoryProductReadSideRepository>();
// Register query dispatcher.
services.AddSingleton<IQueryAsyncDispatcher>((serviceProvider) =>
{
// This object implements IQueryHandlerResolver.
var registration = new QueryHandlerRegistration();
registration.Register(() => new QueryProductByIdHandler(serviceProvider.GetRequiredService<IProductReadSideRepository>()));
return new QueryDispatcher(registration);
});
...
}// This method gets called by the runtime. Use this method to add services to the container.
public void ConfigureServices(IServiceCollection services)
{
...
// Read-side repository.
services.AddSingleton<IProductReadSideRepository, InMemoryProductReadSideRepository>();
// Register query handlers to the container.
// Tip: You can use assembly scanners to scan for handlers.
services.AddTransient<IQueryHandler<QueryProductById, Product>, SyncQueryProductByIdHandler>();
// Register query dispatcher.
services.AddSingleton<IQueryAsyncDispatcher>((serviceProvider) =>
// The ContainerQueryHandlerResolver only resolves sync handlers.
// For async handlers, ContainerQueryAsyncHandlerResolver should be used.
new QueryDispatcher(new ContainerQueryHandlerResolver(new AspNetCoreServiceProviderAdapter(serviceProvider)))
);
...
}
// Container adapter.
class AspNetCoreServiceProviderAdapter : Xer.Cqrs.QueryStack.Resolvers.IContainerAdapter
{
private readonly IServiceProvider _serviceProvider;
public AspNetCoreServiceProviderAdapter(IServiceProvider serviceProvider)
{
_serviceProvider = serviceProvider;
}
public T Resolve<T>() where T : class
{
return _serviceProvider.GetService<T>();
}
}// This method gets called by the runtime. Use this method to add services to the container.
public void ConfigureServices(IServiceCollection services)
{
...
// Read-side repository.
services.AddSingleton<IProductReadSideRepository, InMemoryProductReadSideRepository>();
// Register query handler resolver. This is resolved by QueryDispatcher.
services.AddSingleton<IQueryAsyncDispatcher>((serviceProvider) =>
{
// This implements IQueryHandlerResolver.
var attributeRegistration = new QueryHandlerAttributeRegistration();
// Register all methods with [QueryHandler] attribute.
attributeRegistration.Register(() => new QueryProductByIdHandler(serviceProvider.GetRequiredService<IProductReadSideRepository>()));
return new QueryDispatcher(attributeRegistration);
});
...
}After setting up the query dispatcher in the IoC container, queries can now be dispatched by simply doing:
...
private readonly IQueryAsyncDispatcher _queryDispatcher;
public ProductsController(IQueryAsyncDispatcher queryDispatcher)
{
_queryDispatcher = queryDispatcher;
}
[HttpGet("{productId}")]
public async Task<IActionResult> GetProduct(int productId)
{
Product product = await _queryDispatcher.DispatchAsync<QueryProductById, Product>(new QueryProductById(productId));
if(product != null)
{
return Ok(product);
}
return NotFound();
}
...
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